Undesired heat loss from production tubing as well as uncontrolled heat transfer to outer annuli can be detrimental to the mechanical integrity of outer annuli, cause productivity losses from the well, increase deposition of paraffin and asphaltene materials, accelerate the formation of gas hydrates and destabilize the permafrost in arctic type regions.
Environmentally friendly wellbore insulating fluids developed in the last several years have been very efficient in minimizing heat loss and reducing heat transfer in the well. When introduced into an annulus or riser, such fluids effectively reduce undesired heat loss from the production tubing and/or heat transfer to the outer annuli. Such fluids typically function as packer fluids by insulating the producing fluid. In some cases, heat loss from the produced fluids due to conduction and convection can be reduced by more than 90% when compared with conventional packer fluids.
Non-crosslinked insulating fluids are useful in securing the insulation of wellbore to reduce the heat transfer from the production tubing to the surrounding wellbore, internal annuli, and the riser environment are disclosed in U.S. Pat. No. 6,489,270. The fluid viscosity of such insulating fluids makes it easier to pump the fluid into the annulus; the fluid density of such fluids being controlled by the amount and type of dissolved salt. Such salt is needed to provide positive control of the wellbore pressure without the risk of solid settling and separation. Heat transfer in the well is minimized as evident by the heat retention of the produced fluid.
Fluids having improved insulation properties have further been reported in U.S. Patent Publication No. 2004/0059054 A1. Such fluids containing superabsorbent polymers provide a viscous fluid with low heat transfer coefficient and low convection velocity. The cool-down time, i.e., the time required for the produced hydrocarbon to cool down to the temperature for paraffin, asphaltene and hydrate formation after production is interrupted, however is often shorter than desired.
Alternative fluids having improved insulation properties and methods of using such fluids continue to be sought wherein the fluids are environmentally friendly, exhibit low heat transfer coefficient and further exhibit a longer cool-down time than seen in the fluids of the prior art. In addition, such alternative fluids need to be capable of securing the insulation of the wellbore while reducing the amount of heat transfer from the production tubing to the surrounding wellbore, internal annuli and riser.